High atop an Irish mountain, the massive stone walls of an ancient royal fortress still whisper the secrets of forgotten kings, despite being deliberately dismantled stone by stone nearly a thousand years ago in an act of political revenge.

A ruined tower house on the banks of the River Crana stands as the symbol of the O'Doherty clan's 300-year rule over Inishowen.

A grand Tudor Revival castle was blown to bits in the 1940s for a hydro-electric scheme, only for engineers to discover the waters would never have reached it anyway.

A medieval fortress on the edge of Sheephaven Bay that sheltered Spanish Armada survivors and witnessed some of the bloodiest conflicts in Irish history.

Founded in 1516 by Owen Roe MacSweeney for the Carmelite Order, Rathmullan Priory in County Donegal stands as a fascinating example of how religious buildings were repurposed during Ireland's tumultuous post-Reformation period.

The mid-nineteenth century Lough Eske Castle sits on layers of history, quite literally.

Donegal Castle stands as a fascinating blend of Gaelic and English architectural heritage, positioned strategically where the River Eske meets Donegal Bay.

The town of Donegal sits at the head of Donegal Bay, overlooking the broad, shallow estuary where the River Eske meets the sea.

The Penal Laws (1695-1756) restricted Catholic religious practice in Ireland. During this period, Catholic worship moved to outdoor locations, with natural rock formations and boulders serving as altars for Mass.

In the rolling pastures of Kilclooney More, County Donegal, an oval enclosure marks what archaeologists believe to be an early ecclesiastical site.

In the townland of Kilclooney More in County Donegal, an oval-shaped enclosure marks what archaeologists believe to be an early ecclesiastical site.

In the gently rolling countryside south of the River Deel in County Donegal, a modest hill holds layers of history beneath its grassy surface.

In the townland of Ballycharry, County Donegal, sits a house whose origins remain something of a mystery.

In the townland of Carrowblagh Or Leckemy in County Donegal sits an intriguing piece of Ireland's built heritage; a house whose exact age remains a mystery to archaeologists and historians.

In the townland of Carrowblagh Or Leckemy in County Donegal stands a sweathouse, one of Ireland's lesser-known archaeological treasures.